Non-aqueous pigmented inkjet inks

ABSTRACT

A non-aqueous inkjet ink includes C.I. Pigment Yellow 150 and a polymeric dispersant according to Formula (I): wherein, T represents hydrogen or a polymerization terminating group; Z represents the residue of polyethyleneimine having a number-average molecular weight of at least 100; A represents an oxyalkylene carbonyl group; T-C(O)An- represents a TPOAC-chain which is bound to Z through an amide bond; and n and m are integers wherein m is at least 2 and n is from 2 to 100; the polymeric dispersant fulfills the conditions of: WTPOAC&gt;57 and NAmide≧65 mol % wherein WTPOAC represents the ratio of the weight percentage of TPOAC-chains over the weight percentage of amide bonds in the polymeric dispersant; NAmide represents the mol % of amide bonds based on the total nitrogen content of the polymeric dispersant; and the values of WTPOAC and NAmide are calculated from the total nitrogen content determined by dry combustion of the polymeric dispersant and from the amine content determined through potentiometric titration in a mixture of CH3COOH:THF (14.5:0.5) with 0.1N aqueous perchloric acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2007/060487, filed Oct. 2, 2007. This application claims thebenefit of U.S. Provisional Application No. 60/829,572, filed Oct. 16,2006, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 06122091.9, filed Oct. 11, 2006, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stable inkjet inks comprising a yellowpigment in a non-aqueous medium.

2. Description of the Related Art

Pigment dispersions are made using a dispersant. A dispersant is asubstance for promoting the formation and stabilization of a dispersionof pigment particles in a dispersion medium. Dispersants are generallysurface-active materials having an anionic, cationic or non-ionicstructure. The presence of a dispersant substantially reduces thedispersing energy required. Dispersed pigment particles may have atendency to re-agglomerate after the dispersing operation, due to mutualattraction forces. The use of dispersants also counteracts thisre-agglomeration tendency of the pigment particles.

The dispersant has to meet particularly high requirements when used forinkjet inks. Inadequate dispersing manifests itself as increasedviscosity in liquid systems, loss of brilliance and/or hue shifts.Moreover, particularly good dispersion of the pigment particles isrequired to ensure unimpeded passage of the pigment particles throughthe nozzles of the print head in an inkjet printer, which are usuallyonly a few micrometers in diameter. In addition, pigment particleagglomeration and the associated blockage of the printer nozzles has tobe avoided in the standby periods of the printer.

Many polymeric dispersants contain in one part of the molecule so-calledanchor groups, which adsorb onto the pigments to be dispersed. In aspatially separate part of the molecule, polymeric dispersants havepolymer chains sticking out whereby pigment particles are madecompatible with the dispersion medium, i.e. stabilized.

The properties of polymeric dispersants depend on both the nature of themonomers and their distribution in the polymer. Polymeric dispersantsobtained by statistically polymerizing monomers (e.g. monomers A and Bpolymerized into ABBAABAB) or by polymerizing alternating monomers (e.g.monomers A and B polymerized into ABABABAB) generally result in poordispersion stability. Improvements in dispersion stability were obtainedusing graft copolymer and block copolymer dispersants.

In the design of polymeric dispersants for pigment dispersions,dispersants which contain a polyester chain moiety derived from one ormore hydroxycarboxylic acids or lactones thereof have been known for along time. Early examples of such dispersants are disclosed in EP0158406 A (ICI) for dispersing finely divided particles of a magneticmaterial in an organic liquid.

These are generally of two distinct chemical types. In the first type,the hydroxycarboxylic acid or lactone is polymerized in the presence ofan alkylcarboxylic acid as polymerization terminating group to give apolyester chain having a free carboxylic acid which is then reacted withan amine such as polyethyleneimine.

In the second type of dispersant, the hydroxycarboxylic acid or lactoneis polymerized in the presence of an aliphatic alcohol as polymerizationterminating group to give a polyester chain having a free hydroxyl groupwhich is subsequently converted to a phosphate ester. Early examples ofsuch dispersants are disclosed in EP 0164817 A (ICI).

More recently, the properties of such dispersants have been improved bybranching the alkylene group of the polyester chain as disclosed in U.S.Pat. No. 6,197,877 (ZENECA) or by using polymerization terminatinggroups containing a branched aliphatic chain as disclosed in US2003181544 (AVECIA).

Generally pigments have a non-polar surface. In aqueous inkjet inks, thepolymeric dispersants generally contain hydrophobic anchor groupsexhibiting a high affinity for the pigment surface and hydrophilicpolymer chains for stabilizing the pigments in the aqueous dispersionmedium. The preparation of thermally stable dispersions with submicronparticles is often more difficult in the case of non-aqueous inkjet inkswhere both the pigment surface and the dispersion medium are non-polar.Especially quinacridone pigments and yellow pigments, such as C.I.Pigment Yellow 120, C.I. Pigment Yellow 213 and C.I. Pigment Yellow 150,pose difficulties.

For consistent image quality, the inkjet ink should be capable ofdealing with elevated temperatures during transport of the ink to acustomer and also during inkjet printing where the inkjet ink isgenerally heated to a temperature above 40° C.

Non-aqueous inkjet inks, especially radiation curable inkjet inks, areprinted on a wide variety of substrates requiring different compositionsof the liquid carrier to have adequate adhesion properties onto thedifferent substrates. Usually a concentrated pigment dispersion is madewhich is then diluted with a specific liquid carrier for a certaininkjet application. It has been observed that while in a number of casesthe dilution of the concentrated pigment dispersion results in stableinkjet inks, in a number of other cases the dilution results in inkjetinks of poor dispersion quality and stability.

Preparing different concentrated pigment dispersions is not only a timeconsuming and costly activity in the development of inkjet inks but alsorestricts the flexibility in ink manufacturing requiring theavailability of stocks of different pigment dispersions to guaranteedeliverability of ink.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide non-aqueous inkjet inks which can beprepared from the same concentrated pigment dispersion without loss ofdispersion quality or stability.

Another preferred embodiment of the present invention providesnon-aqueous inkjet inks and ink sets improved for dispersion quality andstability.

Further advantages and benefits of the preferred embodiments of thepresent invention will become apparent from the description hereinafter.

The pigment C.I. Pigment Yellow 150 could be dispersed into aconcentrated pigment dispersion and then diluted with a wide range oforganic solvents exhibiting no significant loss in dispersion qualityand stability using a specific polymeric dispersant.

Advantages and benefits of a preferred embodiment of the presentinvention are realized with a non-aqueous inkjet ink comprising C.I.Pigment Yellow 150 and a polymeric dispersant according to Formula (I):

wherein,T represents hydrogen or a polymerization terminating group;Z represents the residue of polyethyleneimine having a number-averagemolecular weight of at least 100;A represents an oxyalkylene carbonyl group;T-C(O)A_(n)- represents a TPOAC-chain which is bound to Z through anamide bond; andn and m are integers wherein m is at least 2 and n is from 2 to 100;characterized in that the polymeric dispersant fulfills the conditionsof:W _(TPOAC)>57 and N _(Amide)≧65 mol %withW_(TPOAC) representing the ratio of the weight percentage ofTPOAC-chains over the weight percentage of amide bonds in the polymericdispersant;N_(Amide) representing the mol % of amide bonds based on the totalnitrogen content of the polymeric dispersant; andwherein the values of W_(TPOAC) and N_(Amide) are calculated from thetotal nitrogen content determined by dry combustion of the polymericdispersant and from the amine content determined through potentiometrictitration in a mixture of CH₃COOH:THF (14.5:0.5) with 0.1N aqueousperchloric acid.

Another preferred embodiment of the present invention provides anon-aqueous inkjet ink set comprising a stable yellow non-aqueous inkjetink.

It was found that not only C.I. Pigment Yellow 150, but also otherorganic colour pigments could be dispersed into stable non-aqueousinkjet inks using the same polymeric dispersant and liquid carrier. Auniform composition of the different inks in an inkjet ink set is oftenadvantageous since no printing artefacts are to be expected due toincompatibilities between the different components of the inks.

These and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “colorant”, as used in disclosing the present invention, meansdyes and pigments.

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as a colouring agent that is practically insoluble in theapplication medium under the pertaining ambient conditions, hence havinga solubility of less than 10 mg/L therein.

The term “mixed crystal”, which is synonymous for “solid solution”, asused in disclosing the present invention, means a solid, homogeneousmixture of two or more constituents, which may vary in compositionbetween certain limits and remain homogeneous.

The term “C.I.” is used in disclosing the present application as anabbreviation for Colour Index.

The term “actinic radiation” as used in disclosing the presentinvention, means electromagnetic radiation capable of initiatingphotochemical reactions.

The term “spectral separation factor” as used in disclosing the presentinvention means the value obtained by calculating the ratio of themaximum absorbance A_(max) (measured at wavelength λ_(max)) over thereference absorbance A_(ref) determined at a higher wavelength λ_(ref).

The abbreviation “SSF” is used in disclosing the present invention forspectral separation factor.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

Non-Aqueous Inkjet Inks

The non-aqueous inkjet ink according to the present invention containsat least three components: (i) a colour pigment, (ii) a polymericdispersant and (iii) a dispersion medium.

The non-aqueous inkjet ink according to the present invention mayfurther contain at least one surfactant.

The non-aqueous inkjet ink according to the present invention ispreferably an inkjet ink selected from the group consisting of organicsolvent based, oil based and curable pigmented inkjet inks. The curablepigmented inkjet ink is preferably radiation curable. The viscosity ofpigmented inkjet inks is preferably smaller than 100 mPa·s at 30° C. Theviscosity of the pigmented inkjet ink is preferably lower than 30 mPa·s,more preferably lower than 15 mPa·s, and most preferably between 3 and10 mPas all measured at a shear rate of 100 s⁻¹ and a jettingtemperature between 10 and 70° C.

The non-aqueous pigmented inkjet ink according to the present inventionmay contain at least one humectant to prevent the clogging of thenozzle, due to its ability to slow down the evaporation rate of ink.

The curable pigment dispersion may contain as dispersion mediummonomers, oligomers and/or prepolymers possessing different degrees offunctionality. A mixture including combinations of mono-, di-, tri-and/or higher functionality monomers, oligomers or prepolymers may beused. A catalyst called an initiator for initiating the polymerizationreaction may be included in the curable pigmented inkjet ink. Theinitiator can be a thermal initiator, but is preferably aphoto-initiator. The photo-initiator requires less energy to activatethan the monomers, oligomers and/or prepolymers to form the polymer. Thephoto-initiator suitable for use in the curable pigment dispersion maybe a Norrish type I initiator, a Norrish type II initiator or aphoto-acid generator.

Polymeric Dispersants

The polymeric dispersant according to the present invention comprises apolyalkyleneimine core grafted by a number of polyester chain groupsaccording to Formula (I):

wherein,T represents hydrogen or a polymerization terminating group;Z represents the residue of polyethyleneimine having a number-averagemolecular weight of at least 100;A represents an oxyalkylene carbonyl group;T-C(O)A_(n)- represents a TPOAC-chain which is bound to Z through anamide bond; andn and m are integers wherein m is at least 2 and n is from 2 to 100;characterized in that the polymeric dispersant fulfills the conditionsof:W _(TPOAC)>57 and N _(Amide)≧65 mol %withW_(TPOAC) representing the ratio of the weight percentage ofTPOAC-chains over the weight percentage of amide bonds in the polymericdispersant;N_(Amide) representing the mol % of amide bonds based on the totalnitrogen content of the polymeric dispersant; andwherein the values W_(TPOAC) and N_(Amide) are calculated from the totalnitrogen content determined by dry combustion of the polymericdispersant and from the amine content determined through potentiometrictitration in a mixture of CH₃COOH:THF (14.5:0.5) with 0.1N aqueousperchloric acid.

The polymerization terminating group or endgroup T may be derived from amono-carboxylic acid T-COOH selected from the group consisting of analiphatic acid, an aromatic acid, a hetero-aromatic acid, a heterocyclicacid and an alicyclic acid. In a preferred embodiment, the aliphaticacid is a C₁₋₂₅ aliphatic carboxylic acid optionally substituted byhydroxyl, C₁₋₄ alkyl or halogen.

Examples of T-COOH are 2-ethylbutyric, 2-ethylhexanoic, 2-butyloctanoic,2-hexyldecanoic, 2-octyldodecanoic and 2-decyltetradecanoic acids.Branched aliphatic acids of this type are available under the trade markIsocarb (ex Condea GmbH) and specific examples are Isocarb 12, 16, 20,28, 32, 34T and 36. T-COOH may be a single carboxylic acid or may be amixture of such acids.

The compound formed by the (co) polymerisation of a hydroxycarboxylicacid or lactone thereof in the presence of T-COOH can be represented bythe formula:T-CO(O—V—CO)_(n)OHwherein V represents C₁₋₃₀-alkylene and/or C₁₋₃₀-alkenylene and isreferred to hereinafter as a TPOAC-acid.

Examples of hydroxycarboxylic acids are glycolic acid, lactic acid,hydroxyvaleric acid, hydroxycaproic acid, ricinoleic acid,12-hydroxystearic acid, 12-hydroxydodecanoic acid, 5-hydroxydodecanoicacid, 5-hydroxydecanoic acid and 4-hydroxydecanoic acid.

Examples of suitable lactones are β-propiolactone, γ-butyrolactone,optionally alkyl substituted ε-caprolactone and optionally alkylsubstituted δ-valerolactone. The alkyl substituent in ε-caprolactone andδ-valerolactone is preferably C₁₋₆-alkyl and especially C₁₋₄-alkyl andmay be linear or branched. The alkyl substituted ε-caprolactone may beobtained by the oxidation of alkyl substituted cyclohexanone asdescribed in WO 98/19784 and some are obtained as mixtures. Examples ofalkyl substituted ε-caprolactone are 7-methyl, 3-methyl, 5-methyl,6-methyl, 4-methyl, 5-tert-butyl, 4,6,6-trimethyl and 4,4,6-trimethylε-caprolactone. An example of alkyl substituted δ-valerolactone isβ-methyl-δ-valerolactone. Preferred lactones are ε-caprolactone andδ-valerolactone.

In a preferred embodiment, the TPOAC-acid comprises a mixture ofoxyalkylene carbonyl groups derivable from δ-valerolactone andε-caprolactone, more preferably this mixture comprises more than 75 mol% ε-caprolactone.

The polymeric dispersants can be obtained by reacting PEI with aTPOAC-acid or lactone precursor(s) thereof at a temperature between 50and 250° C., preferably in an inert atmosphere and optionally in thepresence of an amidation catalyst. Preferably, the temperature is notless than 80° C. and especially not less than 100° C. In order tominimize charring of the dispersant the temperature is preferably notgreater than 150° C.

The inert atmosphere may be any gas which does not react with the finalproduct or starting materials and includes the inert gases of thePeriodic Table and especially nitrogen.

When the dispersant is prepared in a single stage by reacting PEI,polymerisation terminating agent T-COOH and lactone(s) it is preferableto include an esterification catalyst such as tetra-alkyl titanate, forexample tetrabutyl titanate, zinc salt of an organic acid, for example,zinc acetate, zirconium salt of an aliphatic alcohol, for examplezirconium isopropoxide, toluene sulphonic acid or a strong organic acidsuch as haloacetic acid, for example trifluoroacetic acid. Zirconiumisopropoxide is preferred. When the dispersant of the first aspect ofthe invention is prepared by a single stage process, higher temperaturemay be required and these are typically from 150-180° C.

However, a two-stage process is preferred wherein the TPOAC-acid isprepared separately, prior to reacting it with PEI. In this case, thelactone(s) and polymerisation terminating agent are reacted together inan inert atmosphere at 150-180° C. in the presence of an esterificationcatalyst. The subsequent reaction of the TPOAC-acid with PEI may then becarried out at temperatures of 100-150° C.

An example of the synthesis of the polymeric dispersant having apolyethylenimine core grafted by polyester chains can be represented bythe following condensation reaction of polyethyleneimine with aTPOAC-acid in the presence of a Zr(IV+)isopropoxide catalyst. For thesake of simplicity, polyethylene imine is represented as a linearpolymer chain In the reaction schemes below, although thepolyethyleneimine in accordance with the present invention ishyperbranched and contains a mixture of primary, secondary and tertiaryamines.

Although the reaction seems fairly simple, the synthesis is not thatstraightforward due to the occurrence of side reactions.

A first side reaction which occurs is the PEI (base) catalyzedhydrolyzis of the ester bond in the TPOAC-acid by water:

As a result a TPOAC-acid and an alcohol terminated POAC-acid having ashorter polyester chain length than the original TPOAC-acid are formed,which can both react with the PEI to form a polymeric dispersant. Thereaction may also occur after the TPOAC-acid has already reacted withthe PEI, again resulting in a shorter chain length for the polyestergraft, as shown below:

A second side reaction is a transamidation reaction of the polyesterchains, again leading to shorter chain lengths of the polyester graftson the PEI. The side reaction can occur with free TPOAC chains or withalready condensed TPOAC.

The resulting polymeric dispersant has a hyperbranched polymerarchitecture having a broad distribution of polyester chain lengths,which makes the polymer characterization very difficult. An optimizedschematic representation of part of a polymeric dispersant whereinT-COOH was lauric acid is given by the following formula:

There exist many parameters for designing polymeric dispersantscomprising a polyalkyleneimine core grafted by polyester chains(TPOAC-chains). These parameters include the type of N-containing core(different types of polyalkyleneimine, polyallylamine, polyvinylamine, .. . ), the size of the N-containing core, the number of polyesterchains, the length of the polyester chains, the endgroups of thepolyester chains, the composition of the polyester chains, etc

In spite of the synthetic problems and the many parameters for designingthe polymeric dispersants, it was surprisingly found that there are onlythree crucial parameters:

1. The type of the polyalkyleneimine should be polyethyleneimine (PEI);

2. The polyester chains should be long enough; and

3. The number of polyester chains should be high enough relative to thesize of the PEI.

Parameter 2 (polyester chain length) and parameter 3 (number ofpolyester chains) could be adequately characterized by W_(TPOAC)respectively N_(Amide). W_(TPOAC) represents the ratio of the weightpercentage of TPOAC-chains over the weight percentage of amide bonds inthe polymeric dispersant.

N_(Amide) represents the mol % of amide bonds based on the totalnitrogen content of the polymeric dispersant.

The values of W_(TPOAC) and N_(Amide) can be determined by two simpleanalysis methods. The amine content N_(amine) of the polymericdispersant, expressed as mole amine/100 g of polymeric dispersant, canbe determined through potentiometric titration in a mixture ofCH₃COOH:THF (14.5:0.5) with 0.1N aqueous perchloric acid.

The nitrogen content W_(tot N) of the polymeric dispersant, expressed ingrams nitrogen/100 g polymeric dispersant, can be determined by drycombustion according to DIN ISO13878 (Bodenbeschaffenheit, Bestimmungdes Gesamt-Stickstoffs durch trockene Verbrennung).

Calculation of N_(Amide):

The mole % nitrogen present as an amide bond N_(Amide) based upon thetotal nitrogen content W_(tot N) of the polymeric dispersant is found bythe following formula:N _(Amide)=100×[(W _(tot N)/14)−N _(amine) ]/[W _(tot N)/14]Note: 14=the weight of nitrogen in g/mol.

Calculation of W_(TPOAC):

The weight percentage of PEI present in the polymeric dispersant isfound by the formula (W_(tot N)×43)/14, wherein 43 represents themolecular weight of ethyleneimine in g/mol. The weight percentage of allTPOAC-chains present in the polymeric dispersant is then found by theformula 100−(W_(tot N)×43)/14. The weight percentage of amide bonds inthe polymeric dispersant is obtained by W_(tot N)−(N_(amine)×14).Hence, W _(TPOAC)=[100×(W _(tot N)×43)/14]/[W _(tot N)−(N _(amine)×14)]

The polymeric dispersant according to the present invention must have:W _(TPOAC)>57 and N _(Amide)≧65 mol %.Colour Pigments

The colour pigment in the non-aqueous inkjet ink according to presentinvention is C.I. Pigment Yellow 150.

Pigment particles in inkjet ink should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The average particle size of the pigment in an inkjet ink should bebetween 0.005 and 15 μm. The numeric average pigment particle size ispreferably between 0.005 and 5 μm, more preferably between 0.005 and 1μm, particularly preferably between 0.005 and 0.3 μm and most preferablybetween 0.040 and 0.150 μm.

The pigment is preferably used in the non-aqueous inkjet ink in anamount of 0.1 to 15 wt %, preferably 1 to 10 wt % based on the totalweight of the inkjet ink.

The non-aqueous inkjet ink comprising the pigment C.I. Pigment Yellow150 is generally used in combination with inkjet inks of differentcolours to form an inkjet ink set. These other inkjet inks may be black,cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixturesthereof, and the like.

In a preferred embodiment the inkjet ink set comprises at least a cyanink, a magenta ink, a yellow ink and a black ink. The CMYK ink set mayalso be extended with extra inks such as red, green, blue, and/or orangeto enlarge the colour gamut of the ink set. The CMYK ink set may also beextended by the combination of full density and light density inks ofboth color inks and/or black inks to improve the image quality bylowered graininess.

The pigment is preferably used in the non-aqueous pigment inkjet ink inan amount of 0.1 to 20 wt %, preferably 1 to 10 wt % based on the totalweight of the non-aqueous inkjet ink. In multi-density inkjet ink sets,a light density inkjet ink preferably comprises the pigment in an amountbetween 0.1 to 3 wt % and a full density inkjet ink preferably comprisesthe pigment in an amount between 1 to 10 wt % of pigment.

The colour pigment for the other inkjet inks may be chosen from thosedisclosed by HERBST, Willy, et al. Industrial Organic Pigments,Production, Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN3527305769.

Particular preferred pigments are C.I. Pigment Red 17, 22, 23, 41, 48:1,48:2, 49:1, 49:2, 52:1, 57:1, 81:1, 81:3, 88, 112, 122, 144, 146, 149,169, 170, 175, 176, 184, 185, 188, 202, 206, 207, 210, 216, 221, 248,251, 254, 255, 264, 270, 272 and 282.

Particular preferred pigments are C.I. Pigment Violet 1, 2, 19, 23, 32,37 and 39.

Particular preferred pigments are C.I. Pigment Blue 15:1, 15:2, 15:3,15:4, 15:6, 16, 56, 61 and (bridged) aluminium phthalocyanine pigments.

Particular preferred pigments are C.I. Pigment Orange 5, 13, 16, 34, 40,43, 59, 66, 67, 69, 71 and 73.

Particular preferred pigments are C.I. Pigment Green 7 and 36.

Particular preferred pigments are C.I. Pigment Brown 6 and 7.

Suitable pigments include mixed crystals of the above particularpreferred pigments. A commercially available example is CinquasiaMagenta RT-355-D from Ciba Specialty Chemicals. Mixed crystals are alsoreferred to as solid solutions. Under certain conditions differentcolorants mix with each other to form solid solutions, which are quitedifferent from both physical mixtures of the compounds and from thecompounds themselves. In a solid solution, the molecules of thecomponents enter into the same crystal lattice, usually, but not always,that of one of the components. The x-ray diffraction pattern of theresulting crystalline solid is characteristic of that solid and can beclearly differentiated from the pattern of a physical mixture of thesame components in the same proportion. In such physical mixtures, thex-ray pattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions.

Carbon black is preferred as a pigment for the non-aqueous black inkjetink. Suitable black pigment materials include carbon blacks such asPigment Black 7 (e.g. Carbon Black MA8™ from MITSUBISHI CHEMICAL),REGAL™ 400R, MOGUL™ L, ELFTEX™ 320 from CABOT Co., or Carbon Black FW18,Special Black 250, Special Black 350, Special Black 550, PRINTEX™ 25,PRINTEX™ 35, PRINTEX™ 55, PRINTEX™ 90, PRINTEX™ 150T from DEGUSSA.Additional examples of suitable pigments are disclosed in U.S. Pat. No.5,389,133 (XEROX).

A neutral black inkjet ink can be obtained, for example, by mixingcarbon black with a cyan, a magenta or a cyan and magenta pigment intothe ink, as for example described in pending European patent applicationEP 1593718 A (AGFA).

It is also possible to make mixtures of pigments in a non-aqueous inkjetink. For example, carbon black generally exhibits a warm brownish blacktone, while a neutral black tone is generally preferred. A neutral blackinkjet ink can be obtained, for example, by mixing carbon black with acyan, a magenta or a cyan and magenta pigment into the ink, as forexample described in pending European patent application EP 1593718 A(AGFA). The inkjet application may also require one or more spotcolours, for example for packaging inkjet printing or textile inkjetprinting. Silver and gold are often desired colours for inkjet posterprinting and point-of-sales displays. Particular preferred pigments areC.I. Pigment Metal 1, 2 and 3. Illustrative examples of the inorganicpigments include titanium oxide, barium sulfate, calcium carbonate, zincoxide, lead sulfate, yellow lead, zinc yellow, red iron oxide (III),cadmium red, ultramarine blue, prussian blue, chromium oxide green,cobalt green, amber, titanium black and synthetic iron black.

Dispersion Synergists

The non-aqueous inkjet ink according to the present invention maycontain at least one dispersion synergist. A mixture of dispersionsynergists may be used to further improve dispersion stability.

The dispersion synergist usually consists of an anionic part and acationic part. The anionic part of the dispersion synergist exhibiting acertain molecular similarity with the colour pigment and the cationicpart of the dispersion synergist consists of one or more protons and/orcations to compensate the charge of the anionic part of the dispersionsynergist.

The synergist is preferably added in an amount between 0.1 and 20 wt %based upon the weight of the pigment.

The synergist should be additional to the amount of polymericdispersant(s). The ratio of polymeric dispersant/dispersion synergistdepends upon the pigment and should be determined experimentally.Typically the ratio wt % polymeric dispersant/wt % dispersion synergistis selected between 2:1 to 1000:1, preferably between 2:1 and 100:1.

Suitable dispersion synergists that are commercially available includeSOLSPERSE™ 5000 and SOLSPERSE™ 22000 from NOVEON.

In dispersing C.I. Pigment Blue 15, the use of a sulfonatedCu-phthalocyanine dispersion synergist, e.g. SOLSPERSE™ 5000 from NOVEONis preferred.

Suitable dispersion synergists for non-aqueous inkjet inks in an inkjetink set according to the present invention include those disclosed inpending European Patent Applications EP 05111357 A (AGFA) and EP05111360 A (AGFA).

Dispersion Media

The dispersion medium used is preferably a liquid at room temperature.

In one embodiment the dispersion medium consists of organic solvent(s).Suitable organic solvents include alcohols, ketones, esters, ethers,glycols and polyglycols and derivatives thereof, lactones, N-containingsolvents such as amides, saturated hydrocarbons and unsaturatedhydrocarbons. Preferably mixtures of one or more of these solvents areused.

Examples of suitable alcohols include methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, heptyl alcohol,octyl alcohol, cyclohexyl alcohol, benzyl alcohol, phenylethyl alcohol,phenylpropyl alcohol, furfuryl alcohol, anise alcohol andfluoroalcohols.

Examples of suitable ketones include acetone, methyl ethyl ketone,methyl n-propyl ketone, methyl isopropyl ketone, methyl n-butyl ketone,methyl isobutyl ketone, methyl n-amyl ketone, methyl isoamyl ketone,diethyl ketone, ethyl n-propyl ketone, ethyl isopropyl ketone, ethyln-butyl ketone, ethyl isobutyl ketone, di-n-propyl ketone, diisobutylketone, cyclohexanone, methylcyclohexanone and isophorone,2,4-pentanedione and hexafluoroacetone.

Examples of suitable esters include methyl acetate, ethyl acetate,n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,hexyl acetate, octyl acetate, benzyl acetate, phenoxyethyl acetate,ethyl phenyl acetate, methyl lactate, ethyl lactate, propyl lactate,butyl lactate; methyl propionate, ethyl propionate, benzyl propionate,ethylene carbonate, propylene carbonate, amyl acetate, ethyl benzoate,butyl benzoate, butyl laurate, isopropyl myristate, isopropyl palmirate,triethyl phosphate, tributyl phosphate, diethyl phthalate, dibutylphthalate, diethyl malonate, dipropyl malonate, diethyl succinate,dibutyl succinate, diethyl glutarate, diethyl adipate, dibutyl adipateand diethyl sebacate.

Examples of suitable ethers include butyl phenyl ether, benzyl ethylether, hexyl ether, diethyl ether, dipropyl ether, tetrahydrofuran anddioxane.

Examples of suitable glycols and polyglycols include ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol and tripropylene glycol.

Examples of suitable glycol and polyglycol derivatives include etherssuch as alkylene glycol mono alkyl ethers, alkylene glycol dialkylethers, polyalkylene glycol mono alkyl ethers, polyalkylene glycoldialkyl ethers and esters of the preceding glycol ethers such as acetateand propionate esters, in case of dialkyl ethers only one ether function(resulting in mixed ether/ester) or both ether functions can beesterized (resulting in dialkyl ester).

Examples of suitable alkylene glycol mono alkyl ethers include ethyleneglycol mono methyl ether, ethylene glycol mono ethyl ether, ethyleneglycol mono propyl ether, ethylene glycol mono butyl ether, ethyleneglycol mono hexyl ether, ethylene glycol mono 2-ethyl-hexyl ether,ethylene glycol mono phenyl ether, propylene glycol mono methyl ether,propylene glycol mono ethyl ether, propylene glycol mono n-propyl ether,propylene glycol mono n-butyl ether, propylene glycol mono iso-butylether, propylene glycol mono t-butyl ether and propylene glycol monophenyl ether.

Examples of suitable alkylene glycol dialkyl ethers include ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycolmethyl ethyl ether, ethylene glycol dibutyl ether, propylene glycoldimethyl ether, propylene glycol diethyl ether and propylene glycoldibutyl ether.

Examples of suitable polyalkylene glycol mono alkyl ethers includediethylene glycol mono methyl ether, diethylene glycol mono ethyl ether,diethylene glycol mono-n-propyl ether, diethylene glycol mono n-butylether, diethylene glycol mono hexyl ether, triethylene glycol monomethyl ether, triethylene mono ethyl ether, triethylene glycol monobutyl ether, dipropylene mono methyl ether, dipropylene glycol monoethyl ether, dipropylene glycol n-propyl ether, dipropylene glycol monon-butyl ether, dipropylene mono t-butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol mono ethyl ether, tripropylene glycolmono n-propyl ether and tripropylene glycol mono n-butyl ether.

Examples of suitable polyalkylene glycol dialkyl ethers includediethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether,triethylene glycol diethyl ether, tetraethylene glycol diethyl ether,diethylene glycol methyl ethyl ether, triethylene glycol methyl ethylether, tetraethylene glycol methyl ethyl ether, diethylene glycoldi-n-propyl ether, diethylene glycol di-iso-propyl ether, dipropyleneglycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene din-propyl ether, dipropylene di t-butyl ether, tripropylene glycoldimethyl ether and tripropylene glycol diethyl ether.

Examples of suitable glycol esters include ethylene glycol monomethylether acetate, ethylene glycol monoethyl ether acetate, ethylene glycolmonopropyl ether acetate, ethylene glycol monobutyl ether acetate,diethylene glycol monoethyl ether acetate, diethylene glycol monobutylether acetate, propylene glycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, dipropylene glycol monomethyl etheracetate and propylene glycol monomethyl ether propionate.

Preferred solvents for use in the pigment dispersion and inkjet inksaccording to the present invention are one or more polyalkyleneglycoldialkylethers represented by the formula (PAG)

wherein,R₁ and R₂ are each independently selected from an alkyl group having 1to 4 carbon atoms;Y represents an ethylene group and/or a propylene group; whereinn is an integer selected from 4 to 20 for a first polyalkyleneglycoldialkylether; and n is an integer selected from 5 to 20 for a secondpolyalkyleneglycol.

The alkyl groups R₁ and R₂ of the polyalkyleneglycol dialkylethersaccording to Formula (PAG) preferably represent methyl and/or ethyl.Most preferably the alkyl groups R₁ and R₂ are both methyl groups.

In a preferred embodiment the polyalkyleneglycol dialkylethers accordingto Formula (PAG) are polyethylene glycol dialkylethers.

In another preferred embodiment, a mixture of 2, 3, 4 or morepolyalkyleneglycol dialkylethers, more preferably polyethylene glycoldialkylethers are present in the pigment dispersion or inkjet ink.

Suitable mixtures of polyalkyleneglycol dialkylethers for the pigmentdispersions include mixtures of polyethylene glycol dimethyl ethershaving a molecular weight of at least 200, such as Polyglycol DME 200™,Polyglycol DME 250™ and Polyglycol DME 500™ from CLARIANT. Thepolyalkyleneglycol dialkylethers used in non-aqueous inkjet inks havepreferably an average molecular weight between 200 and 800, and morepreferably no polyalkyleneglycol dialkylethers with a molecular weightof more than 800 are present. The mixture of polyalkyleneglycoldialkylethers is preferably a homogeneous liquid mixture at roomtemperature.

Suitable commercial glycol ether solvents include CELLOSOLVE™ solventsand CARBITOL™ solvents from UNION CARBIDE, EKTASOLVE™ solvents fromEASTMAN, DOWANOL™ solvents from DOW, OXITOLL™ solvents, DIOXITOLL™solvents, PROXITOLL™ solvents and DIPROXITOLL™ solvents from SHELLCHEMICAL and ARCOSOLV™ solvents from LYONDELL.

Lactones are compounds having a ring structure formed by ester bonds andcan be of the γ-lactone (5-membered ring structure), δ-lactone(6-membered ring structure) or ε-lactone (7-membered ring structure)types. Suitable examples of lactones include γ-butyrolactone,γ-valerolactone, γ-hexylactone, γ-heptalactone, γ-octalactone,γ-nonalactone, γ-decalactone, γ-undecalactone, δ-valerolactone,δ-hexylactone, δ-heptalactone, δ-octalactone, δ-nonalactone,δ-decalactone, δ-undecalactone and ε-caprolactone.

Suitable examples of N-containing organic solvents include2-pyrrolidone, N-methylpyrrolidone, N,N-dimethylacetamid,N,N-dimethylformamid, acetonitril and N,N-dimethyldodecanamide.

Examples of suitable hydrocarbons include saturated hydrocarbons such asn-hexane, isohexane, n-nonane, isononane, dodecane and isododecane;unsaturated hydrocarbons such as 1-hexene, 1-heptene and 1-octene;cyclic saturated hydrocarbons such as cyclohexane, cycloheptane,cyclooctane, cyclodecane and decalin; cyclic unsaturated hydrocarbonssuch as cyclohexene, cycloheptene, cyclooctene,1,1,3,5,7-cyclooctatetraene; and cyclododecene; and aromatichydrocarbons such as benzene, toluene and xylene.

In another embodiment the dispersion medium comprises oil types ofliquids, alone or in combination with organic solvent(s).

Suitable organic solvents include alcohols, ketones, esters, ethers,glycols and polyglycols and derivatives thereof, lactones, N-containingsolvents such as amides, higher fatty acid ester and mixtures of one ormore of the solvents as described above for solvent based dispersionmedia.

The amount of polar solvent is preferably lower than the amount of oil.The organic solvent has preferably a high boiling point, preferablyabove 200° C. Examples of suitable combinations are disclosed by EP0808347 (XAAR TECHNOLOGY LTD) especially for the use of oleyl alcoholand EP 1157070 (VIDEOJET TECHNOLOGIES INC) for the combination of oiland volatile organic solvent.

Suitable oils include saturated hydrocarbons and unsaturatedhydrocarbons, aromatic oils, paraffinic oils, extracted paraffinic oils,napthenic oils, extracted napthenic oils, hydro treated light or heavyoils, vegetable oils, white oils, petroleum naphtha oils,halogen-substituted hydrocarbons, silicones and derivatives and mixturesthereof.

Hydrocarbons may be selected from straight chain or branched chainaliphatic hydrocarbons, alicyclic hydrocarbons and aromatichydrocarbons. Examples of hydrocarbons are saturated hydrocarbons suchas n-hexane, isohexane, n-nonane, isononane, dodecane and isododecane;unsaturated hydrocarbons such as 1-hexene, 1-heptene and 1-octene;cyclic saturated hydrocarbons such as cyclohexane, cycloheptane,cyclooctane, cyclodecane and decalin; cyclic unsaturated hydrocarbonssuch as cyclohexene, cycloheptene, cyclooctene,1,1,3,5,7-cyclooctatetraene; and cyclododecene; and aromatichydrocarbons such as benzene, toluene, xylene, naphthalene,phenanthrene, anthracene and derivatives thereof. In literature the termparaffinic oil is often used. Suitable Paraffinic oils can be normalparaffin type (octane and higher alkanes), isoparaffins (isooctane andhigher iso-alkanes) and cycloparaffins (cyclooctane and highercycloalkanes) and mixtures of paraffin oils. The term “liquid paraffin”is often used to refer to a mixture of mainly comprising threecomponents of a normal paraffin, an isoparaffin and a monocyclicparaffin, which is obtained by highly refining a relatively volatilelubricating oil fraction through a sulphuric-acid washing or the like,as described in U.S. Pat. No. 6,730,153 (SAKATA INX CORP.). Suitablehydrocarbons are also described as de-aromatized petroleum distillates.

Suitable examples of halogenated hydrocarbons include methylenedichloride, chloroform, carbon tetra chloromethane and methylchloroform. Other suitable examples of halogen-substituted hydrocarbonsinclude perfluoro-alkanes, fluorine-based inert liquids and fluorocarboniodides.

Suitable examples of silicone oils include dialkyl polysiloxane (e.g.,hexamethyl disiloxane, tetramethyl disiloxane, octamethyl trisiloxane,hexamethyl trisiloxane, heptamethyl trisiloxane, decamethyltetrasiloxane, trifluoropropyl heptamethyl trisiloxane, diethyltetramethyl disiloxane), cyclic dialkyl polysiloxane (e.g., hexamethylcyclotrisiloxane, octamethyl cyclotetrasiloxane, tetramethylcyclotetrasiloxane, tetra(trifluoropropyl)tetramethylcyclotetrasiloxane), and methylphenyl silicone oil.

White oils is a term used for white mineral oils, which are highlyrefined mineral oils that consist of saturated aliphatic and alicyclicnon-polar hydrocarbons. White oils are hydrophobic, colourless,tasteless, odourless, and do not change colour over time.

Vegetable oils include semi-drying oils such as soybean oil, cotton seedoil, sunflower oil, rape seed oil, mustard oil, sesame oil and corn oil;non-drying oils such as olive oil, peanut oil and tsubaki oil; anddrying oils such as linseed oil and safflower oil, wherein thesevegetable oils can be used alone or as a mixture thereof.

Examples of other suitable oils include petroleum oils, non-drying oilsand semi-drying oils.

Commercially available suitable oils include the aliphatic hydrocarbonstypes such as the ISOPAR™ range (isoparaffins) and Varsol/Naphtha rangefrom EXXON CHEMICAL, the SOLTROL™ range and hydrocarbons from CHEVRONPHILLIPS CHEMICAL, and the SHELLSOL™ range from SHELL CHEMICALS.

Suitable commercial normal paraffins include the NORPAR™ range fromEXXON MOBIL CHEMICAL.

Suitable commercial napthenic hydrocarbons include the NAPPAR™ rangefrom EXXON MOBIL CHEMICAL.

Suitable commercial de-aromatized petroleum distillates include theEXXSOL™ D types from EXXON MOBIL CHEMICAL.

Suitable commercial fluoro-substituted hydrocarbons includefluorocarbons from DAIKIN INDUSTRIES LTD, Chemical Division.

Suitable commercial silicone oils include the silicone fluid ranges fromSHIN-ETSU CHEMICAL, Silicone Division.

Suitable commercial white oils include WITCO™ white oils from CROMPTONCORPORATION.

If the non-aqueous pigment dispersion is a curable pigment dispersion,the dispersion medium comprises one or more monomers and/or oligomers toobtain a liquid dispersion medium. Sometimes, it can be advantageous toadd a small amount of an organic solvent to improve the dissolution ofthe dispersant. The content of organic solvent should be lower than 20wt % based on the total weight of the pigment inkjet ink. In othercases, it can be advantageous to add a small amount of water, forexample, to improve the spreading of the inkjet ink on a hydrophilicsurface, but preferably the ink-jet ink contains no water.

Preferred organic solvents include alcohols, aromatic hydrocarbons,ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols,cello solves, higher fatty acid esters. Suitable alcohols include,methanol, ethanol, propanol and 1-butanol, 1-pentanol, 2-butanol,t.-butanol. Suitable aromatic hydrocarbons include toluene, and xylene.Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone,2,4-pentanedione and hexafluoroacetone. Also glycol, glycolethers,N-methylpyrrolidone, N,N-dimethylacetamid, N,N-dimethylformamid may beused.

Suitable monomers and oligomers can be found in Polymer Handbook, Vol.1+2. 4th edition. Edited by J. BRANDRUP, et al. Wiley-Interscience,1999.

Any polymerizable compound commonly known in the art may be employed.Particularly preferred for use as a radiation curable compound in theradiation curable inkjet ink are monofunctional and/or polyfunctionalacrylate monomers, oligomers or prepolymers, such as isoamyl acrylate,stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate,isoamylstyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycolacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalicacid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate,methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate,methoxypropylene glycol acrylate, phenoxyethyl acrylate,tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate,vinyl ether acrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyxyethylphthalic acid, 2-acryloxyethyl-2-hydroxyethyl-phthalicacid, lactone modified flexible acrylate, and t-butylcyclohexylacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, dipropylene glycoldiacrylate, tripropylene glycol diacrylate, polypropylene glycoldiacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, neopentyl glycol diacrylate,dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide)adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate,hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentylglycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate andpolytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EOmodified trimethylolpropane triacrylate, tri (propylene glycol)triacrylate, caprolactone modified trimethylolpropane triacrylate,pentaerythritol triacrylate, pentaerithritol tetraacrylate,pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate,ditrimethylolpropane tetraacrylate, glycerinpropoxy triacrylate, andcaprolactam modified dipentaerythritol hexaacrylate, or an N-vinylamidesuch as, N-vinylcaprolactam or N-vinylformamide or acrylamide or asubstituted acrylamide, such as acryloylmorpholine.

Other suitable monofunctional acrylates include caprolactone acrylate,cyclic trimethylolpropane formal acrylate, ethoxylated nonyl phenolacrylate, isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate,alkoxylated phenol acrylate, tridecyl acrylate and alkoxylatedcyclohexanone dimethanol diacrylate.

Other suitable difunctional acrylates include alkoxylated cyclohexanonedimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate and neopentyl glycoldiacrylate.

Other suitable trifunctional acrylates include propoxylated glycerinetriacrylate and propoxylated trimethylolpropane triacrylate.

Other higher functional acrylates include di-trimethylolpropanetetraacrylate, dipentaerythritol pentaacrylate, ethoxylatedpentaeryhtitol tetraacrylate, methoxylated glycol acrylates and acrylateesters.

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, hydroxyethyl methacrylate, phenoxyethyl methacrylate,cyclohexyl methacrylate, tetraethylene glycol dimethacrylate, andpolyethylene glycol dimethacrylate are preferred due to their relativelyhigh sensitivity and higher adhesion to an ink-receiver surface.

Furthermore, the inkjet inks may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Suitable examples of styrene compounds are styrene, p-methylstyrene,p-methoxystyrene, b-methylstyrene, p-methyl-b-methylstyrene,a-methylstyrene and p-methoxy-b-methylstyrene.

Suitable examples of vinylnaphthalene compounds are 1-vinylnaphthalene,a-methyl-1-vinylnaphthalene, b-methyl-1-vinylnaphthalene,4-methyl-1-vinylnaphthalene and 4-methoxy-1-vinylnaphthalene.

Suitable examples of N-vinyl heterocyclic compounds areN-vinylcarbazole, N-vinylpyrrolidone, N-vinylindole, N-vinylpyrrole,N-vinylphenothiazine, N-vinylacetoanilide, N-vinylethylacetoamide,N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam andN-vinylimidazole.

The cationically polymerizable compound of the inkjet ink can be one ormore monomers, one or more oligomers or a combination thereof.

Suitable examples of cationically curable compounds can be found inAdvances in Polymer Science, 62, pages 1 to 47 (1984) by J. V. Crivello.

The cationic curable compound may contain at least one olefin,thioether, acetal, thioxane, thietane, aziridine, N, O, S or Pheterocycle, aldehyde, lactam or cyclic ester group.

Examples of cationic polymerizable compounds include monomers and/oroligomers epoxides, vinyl ethers, styrenes, oxetanes, oxazolines,vinylnaphthalenes, N-vinyl heterocyclic compounds, tetrahydrofurfurylcompounds.

The cationically polymerizable monomer can be mono-, di- ormulti-functional or a mixture thereof.

Suitable cationic curable compounds having at least one epoxy group arelisted in the “Handbook of Epoxy Resins” by Lee and Neville, McGraw HillBook Company, New York (1967) and in “Epoxy Resin Technology” by P. F.Bruins, John Wiley and Sons New York (1968).

Examples of cationic curable compounds having at least one epoxy groupinclude 1,4-butanediol diglycidyl ether,3-(bis(gycidyloxymethyl)methoxy)-1,2-propane diol, limonene oxide,2-biphenyl gycidyl ether,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,epichlorohydrin-bisphenol S based epoxides, epoxidized styrenics andmore epichlorohydrin-bisphenol F and A based epoxides and epoxidizednovolaks.

Suitable epoxy compounds comprising at least two epoxy groups in themolecule are alicyclic polyepoxide, polyglycidyl ester of polybasicacid, polyglycidyl ether of polyol, polyglycidyl ether ofpolyoxyalkylene glycol, polyglycidyl ester of aromatic polyol,polyglycidyl ether of aromatic polyol, urethane polyepoxy compound, andpolyepoxy polybutadiene.

Examples of cycloaliphatic diepoxides include copolymers of epoxides andhydroxyl components such as glycols, polyols, or vinyl ether, such as3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexylcarboxylate;bis(3,4-epoxycylohexylmethyl) adipate; limonene diepoxide; diglycidylester of hexahydrophthalic acid.

Examples of vinyl ethers having at least one vinyl ether group includeethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecylvinyl ether, cyclohexyl vinyl ether, butanediol divinyl ether, hydroxylbutyl vinyl ether, cyclohexane dimethanol monovinyl ether, phenyl vinylether, p-methylphenyl vinyl ether, p-methoxyphenyl vinyl ether,a-methylphenyl vinyl ether, b-methylisobutyl vinyl ether andb-chloroisobutyl vinyl ether, diethyleneglycol divinyl ether,triethylene glycol divinyl ether, n-propyl vinyl ether, isopropyl vinylether, dodecyl vinyl ether, diethylene glycol monovinyl ether,cyclohexanedimethanol divinyl ether, 4-(vinyloxy)butyl benzoate,bis[4-(vinyl oxy)butyl]adipate, bis[4-(vinyl oxy)butyl]succinate,4-(vinyloxy methyl)cyclohexylmethyl benzoate,bis[4-(vinyloxy)butyl]isophthalate,bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate,tris[4-(vinyloxy)butyl]trimellitate, 4-(vinyloxy)butyl steatite,bis[4-(vinyloxy)butyl]hexanediylbiscarbamate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]terephthalate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate,bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)-biscarbamate,bis[4-vinyloxy)butyl](methylenedi-4,1-phenylene)biscarbamate and3-amino-1-propanol vinyl ether.

Suitable examples of oxetane compounds having at least one oxetane groupinclude 3-ethyl-3-hydroloxymethyl-1-oxetane, the oligomeric mixture1,4-bis[3-ethyl-3-oxetanyl methoxy)methyl]benzene,3-ethyl-3-phenoxymethyl-oxetane, bis ([1-ethyl(3-oxetanil)]methyl)ether,3-ethyl-3-[(2-ethylhexyloxy)methyl]oxetane, 3-ethyl-[(tri-ethoxysilylpropoxy)methyl]oxetane and 3,3-dimethyl-2(p-methoxy-phenyl)-oxetane.

Initiators

A curable inkjet ink usually contains an initiator. The initiatortypically initiates the polymerization reaction. The initiator can be athermal initiator, but is preferably a photo-initiator. Thephoto-initiator requires less energy to activate than the monomers,oligomers and/or prepolymers to form the polymer. The photo-initiatorsuitable for use in the curable liquids may be a Norrish type Iinitiator, a Norrish type II initiator or a photo-acid generator.

Thermal initiator(s) suitable for use in the curable inkjet ink includetert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid),1,1′-azobis(cyclohexanecarbonitrile), 2,2′-azobisisobutyronitrile(AIBN), benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane,1,1-bis(tert-butylperoxy)cyclohexane,1,1-Bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne,bis(1-(tert-butylperoxy)-1-methylethyl)benzene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylhydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butylperoxybenzoate, tert-butylperoxy isopropyl carbonate, cumenehydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroylperoxide, 2,4-pentanedione peroxide, peracetic acid and potassiumpersulfate.

The photo-initiator or photo-initiator system absorbs light and isresponsible for the production of initiating species, such as freeradicals and cations. Free radicals and cations are high-energy speciesthat induce polymerization of monomers, oligomers and polymers and withpolyfunctional monomers and oligomers thereby also induce cross-linking.

Irradiation with actinic radiation may be realized in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of photo-initiator together.

A combination of different types of initiator, for example, aphoto-initiator and a thermal initiator can also be used.

A preferred Norrish type I-initiator is selected from the groupconsisting of benzoinethers, benzil ketals, α,α-dialkoxyacetophenones,α-hydroxyalkylphenones, α-aminoalkylphenones, acylphosphine oxides,acylphosphine sulphides, α-haloketones, α-halosulfones andα-halophenylglyoxalates.

A preferred Norrish type II-initiator is selected from the groupconsisting of benzophenones, thioxanthones, 1,2-diketones andanthraquinones. A preferred co-initiator is selected from the groupconsisting of an aliphatic amine, an aromatic amine and a thiol.Tertiary amines, heterocyclic thiols and 4-dialkylamino-benzoic acid areparticularly preferred as co-initiator.

Suitable photo-initiators are disclosed in CRIVELLO, J. V., et al.VOLUME III: Photoinitiators for Free Radical Cationic. 2nd edition.Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p.287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphineoxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1,2-diphenylethan-1-one or 5,7-diiodo-3-butoxy-6-fluorone,diphenyliodonium fluoride and triphenylsulfonium hexafluophosphate.

Suitable commercial photo-initiators include IRGACURE™ 184, IRGACURE™500, IRGACURE™ 907, IRGACURE™ 369, IRGACURE™ 1700, IRGACURE™ 651,IRGACURE™ 819, IRGACURE™ 1000, IRGACURE™ 1300, IRGACURE™ 1870, DAROCUR™1173, DAROCUR™ 2959, DAROCUR™ 4265 and DAROCUR™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin TPO available from BASF AG, ESACURE™ KT046,ESACURE™ KIP150, ESACURE™ KT37 and ESACURE™ EDB available from LAMBERTI,H-NU™ 470 and H-NU™ 470X available from SPECTRA GROUP Ltd.

Suitable cationic photo-initiators include compounds, which form aproticacids or Bronstead acids upon exposure to ultraviolet and/or visiblelight sufficient to initiate polymerization. The photo-initiator usedmay be a single compound, a mixture of two or more active compounds, ora combination of two or more different compounds, i.e. co-initiators.Non-limiting examples of suitable cationic photo-initiators arearyldiazonium salts, diaryliodonium salts, triarylsulphonium salts,triarylselenonium salts and the like.

The curable inkjet ink may contain a photo-initiator system containingphoto-initiator(s) and one or more sensitizers that transfer energy tothe photo-initiator(s). Suitable sensitizers include photoreduciblexanthene, fluorene, benzoxanthene, benzothioxanthene, thiazine, oxazine,coumarin, pyronine, porphyrin, acridine, azo, diazo, cyanine,merocyanine, diarylmethyl, triarylmethyl, anthraquinone,phenylenediamine, benzimidazole, fluorochrome, quinoline, tetrazole,naphthol, benzidine, rhodamine, indigo and/or indanthrene dyes. Theamount of the sensitizer is in general from 0.01 to 15 wt %, preferablyfrom 0.05 to 5 wt %, based in each case on the total weight of thecurable pigmented inkjet ink.

In order to increase the photosensitivity further, the curable pigmentedinkjet inks may additionally contain co-initiators. For example, thecombination of titanocenes and trichloromethyl-s-triazines, oftitanocenes and ketoxime ethers and of acridines andtrichloromethyl-s-triazines is known. A further increase in sensitivitycan be achieved by adding dibenzalacetone or amino acid derivatives. Theamount of co-initiator or co-initiators is in general from 0.01 to 20 wt%, preferably from 0.05 to 10 wt %, based in each case on the totalweight of the curable pigmented inkjet ink.

A preferred initiator system is2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-(7CI, 8CI)4,4′-Bi-4H-imidazole corresponding to the chemical formula:

in the presence of a co-initiator such as 2-mercapto benzoxazole.

Another preferred type of initiator is an oxime ester. A suitableexample has as chemical formula:

A preferred amount of initiator is 0.3-50 wt % of the total weight ofthe curable pigmented inkjet ink, and more preferably 1-15 wt % of thetotal weight of the curable pigmented inkjet ink.

Inhibitors

Radiation curable inkjet inks according to the present invention maycontain a polymerization inhibitor. Suitable polymerization inhibitorsinclude phenol type antioxidants, hindered amine light stabilizers,phosphor type antioxidants, hydroquinone monomethyl ether commonly usedin (meth)acrylate monomers, and hydroquinone, t-butylcatechol,pyrogallol may also be used.

Suitable commercial inhibitors are, for example, SUMILIZER™ GA-80,SUMILIZER™ GM and SUMILIZER™ GS produced by Sumitomo Chemical Co. Ltd.;GENORAD™ 16, GENORAD™ 18 and GENORAD™ 20 from Rahn A G; IRGASTAB™ UV10and IRGASTAB™ UV22, TINUVIN™ 460 and CGS20 from Ciba SpecialtyChemicals; FLOORSTAB™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd. ADDITOL™ S range (S100, S110, S120 and S130) from CytecSurface Specialties.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization is determined prior to blending. The amountof a polymerization inhibitor is preferably lower than 2 wt % of thetotal ink.

Surfactants

The pigmented inkjet ink according to the present invention may containat least one surfactant. The surfactant(s) can be anionic, cationic,non-ionic, or zwitter-ionic and are usually added in a total quantityless than 20 wt % based on the total weight of the pigmented inkjet inkand particularly in a total less than 10 wt % based on the total weightof the pigmented inkjet ink.

Suitable surfactants for the pigmented inkjet ink according to thepresent invention include fatty acid salts, ester salts of a higheralcohol, alkylbenzene sulphonate salts, sulphosuccinate ester salts andphosphate ester salts of a higher alcohol (for example, sodiumdodecylbenzenesulphonate and sodium dioctylsulphosuccinate), ethyleneoxide adducts of a higher alcohol, ethylene oxide adducts of analkylphenol, ethylene oxide adducts of a polyhydric alcohol fatty acidester, and acetylene glycol and ethylene oxide adducts thereof (forexample, polyoxyethylene nonylphenyl ether, and SURFYNOL™ 104, 104H,440, 465 and TG available from AIR PRODUCTS & CHEMICALS INC.).

For non-aqueous inkjet inks preferred surfactants are selected fromfluoro surfactants (such as fluorinated hydrocarbons), silicones andsiloxanes. The silicones may be polyether modified, polyether modifiedhydroxy functional, amine modified, epoxy modified and othermodifications or combinations thereof. The siloxanes may be alkoxylated.Preferred silicones and siloxanes are polymeric, for examplepolydimethylsilicones and polydimethylsiloxanes.

When the pigmented inkjet ink is a radiation curable inkjet ink afluorinated or silicone compound may be used as a surfactant, preferablya cross-linkable surfactant is used. Polymerizable monomers havingsurface-active effects include silicone modified acrylates, siliconemodified methacrylates, acrylated siloxanes, polyether modified acrylicmodified siloxanes, fluorinated acrylates, and fluorinatedmethacrylates. Polymerizable monomers having surface-active effects canbe mono-, di-, tri- or higher functional (meth)acrylates or mixturesthereof.

Other Additives

In addition to the constituents, described above, the pigmented inkjetinks may, if necessary, further contain following additives to havedesired performance: UV-absorbers, evaporation accelerators, rustinhibitors, crosslinking agents, soluble electrolytes as conductivityaid, sequestering agents and chelating agents, compounds to introducesecurity features, . . . .

Compounds to introduce security features include a fluorescent compound,a phosphorescent compound, a thermochromic compound, an iridescentcompound and a magnetic particle. Suitable UV-fluorescent andphosphorescent compounds include LUMILUX™ luminescent pigments fromHONEYWELL, UVITEX™ OB from CIBA-GEIGY, KEYFLUOR™ dyes and pigments fromKEYSTONE and fluorescent dyes from SYNTHEGEN.

Preparation of Inkjet Inks

The inkjet ink may be prepared by precipitating or milling the pigmentin the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy. A combination of these techniques maybe used.

Many different types of materials may be used as milling media, such asglasses, ceramics, metals, and plastics. In a preferred embodiment, thegrinding media can comprise particles, preferably substantiallyspherical in shape, e.g. beads consisting essentially of a polymericresin or yttrium stabilized zirconium oxide beads.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and for radiationcurable inkjet inks as much as possible under light conditions in whichactinic radiation has been substantially excluded.

The inkjet ink according to the present invention may contain more thanone pigment, the inkjet ink may be prepared using separate dispersionsfor each pigment, or alternatively several pigments may be mixed andco-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture comprise the millgrind and the milling media. The mill grind comprises pigment, polymericdispersant and a liquid carrier. For inkjet inks, the pigment is usuallypresent in the mill grind at 1 to 50 wt %, excluding the milling media.The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. In the present invention pigmentdispersions with an average particle size of less than 100 nm may beprepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g. for a bead mill. The milled pigment concentrate is preferablyseparated from the milling media by filtration.

In general it is desirable to make the inkjet inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the inkjet printing system. Thistechnique permits preparation of a greater quantity of pigment ink fromthe equipment. By dilution, the inkjet ink is adjusted to the desiredviscosity, surface tension, colour, hue, saturation density, and printarea coverage for the particular application.

Inkjet Printers

The non-aqueous inkjet ink according to the present invention may bejetted by one or more printing heads ejecting small droplets of liquidin a controlled manner through nozzles onto an ink-receiver surface,which is moving relative to the printing head(s).

A preferred printing head for the inkjet printing system is apiezoelectric head. Piezoelectric inkjet printing is based on themovement of a piezoelectric ceramic transducer when a voltage is appliedthereto. The application of a voltage changes the shape of thepiezoelectric ceramic transducer in the printing head creating a void,which is then filled with ink. When the voltage is again removed, theceramic expands to its original shape, ejecting a drop of ink from theprint head. However the inkjet printing method is not restricted topiezoelectric inkjet printing. Other inkjet printing heads can be usedand include various types, such as a continuous type and thermal,electrostatic and acoustic drop on demand type.

At high printing speeds, the inks must be ejected readily from theprinting heads, which puts a number of constraints on the physicalproperties of the ink, e.g. a low viscosity at the jetting temperature,which may vary from 25° C. to 110° C., a surface energy such that theprinting head nozzle can form the necessary small droplets, a homogenousliquid capable of rapid conversion to a dry printed area, . . . .

The viscosity of the inkjet ink used in the ink-jet printing methodaccording to the present invention is preferably lower than 30 mPa·s,more preferably lower than 15 mPa·s, and most preferably between 2 and10 mPas at a shear rate of 100 s⁻¹ and a jetting temperature between 10and 70° C.

The inkjet printing head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing ispreferred for obtaining a high areal throughput. Another preferred printmode is printing in a “single pass printing process”, which can beperformed by using page wide inkjet printing heads or multiple staggeredinkjet printing heads which cover the entire width of the ink-receiversurface. In a single pass printing process the inkjet printing headsusually remain stationary and the ink-receiver surface is transportedunder the inkjet printing heads.

Spectral Separation Factor

The spectral separation factor SSF was found to be an excellent measureto characterize a pigmented inkjet ink, as it takes into accountproperties related to light-absorption (e.g. wavelength of maximumabsorbance λ_(max), shape of the absorption spectrum andabsorbance-value at λ_(max)) as well as properties related to thedispersion quality and stability.

A measurement of the absorbance at a higher wavelength gives anindication on the shape of the absorption spectrum. The dispersionquality can be evaluated based on the phenomenon of light scatteringinduced by solid particles in solutions. When measured in transmission,light scattering in pigment inks may be detected as an increasedabsorbance at higher wavelengths than the absorbance peak of the actualpigment. The dispersion stability can be evaluated by comparing the SSFbefore and after a heat treatment of e.g. a week at 80° C.

The spectral separation factor SSF of the ink is calculated by using thedata of the recorded spectrum of an ink solution or a jetted image on asubstrate and comparing the maximum absorbance to the absorbance at ahigher reference wavelength λ_(ref). The spectral separation factor iscalculated as the ratio of the maximum absorbance A_(max) over theabsorbance A_(ref) at a reference wavelength.

${SSF} = \frac{A_{{ma}\; x}}{A_{ref}}$

The SSF is an excellent tool to design inkjet ink sets with large colourgamut. Often inkjet ink sets are now commercialized, wherein thedifferent inks are not sufficiently matched with each other. Forexample, the combined absorption of all inks does not give a completeabsorption over the whole visible spectrum, e.g. “gaps” exist betweenthe absorption spectra of the colorants. Another problem is that one inkmight be absorbing in the range of another ink. The resulting colourgamut of these inkjet ink sets is low or mediocre.

EXAMPLES

The present invention will now be described in detail by way of Exampleshereinafter.

Materials

All materials used in the following examples were readily available fromstandard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS(Belgium) unless otherwise specified.

PV19 is HOSTAPERM™ Red E5B02, a C.I. Pigment Violet 19 from CLARIANT.

PV19/PR202 is CHROMOPHTAL™ Jet Magenta 3BC2, a mixed crystal of C.I.Pigment Violet 19 and C.I. Pigment Red 202 from CIBA SPECIALTYCHEMICALS.

PB15:4 is HOSTAPERM™ Blue P-BFS, a C.I. Pigment Blue 15:4 from CLARIANT.

PY4 is ACETANIL™ 10 GO 0415C, a C.I. Pigment Yellow 4 from CAPPELLEPIGMENTS N.V.

PY12 is PERMANENT™ Yellow DHG M250, a C.I. Pigment Yellow 12 fromCLARIANT.

PY14 is SUNBRITE™ Yellow 14, a C.I. Pigment Yellow 14 from SUN CHEMICAL.

PY74 is HANSA™ Brilliant Yellow 5GX 03, a C.I. Pigment Yellow 74 fromCLARIANT.

PY81 is NOVOPERM™ Yellow H10G 01, a C.I. Pigment Yellow 81 fromCLARIANT.

PY83 is NOVOPERM™ Yellow P-HR 07 VP2436, a C.I. Pigment Yellow 83 fromCLARIANT.

PY93 is HEUBACH™ Gelb 109300, a C.I. Pigment Yellow 93 from HEUBACHGmbH.

PY95 is CHROMOPHTAL™ Yellow GR, a C.I. Pigment Yellow 95 from CIBASPECIALTY CHEMICALS.

PY97 is NOVOPERM™ Yellow FGL, a C.I. Pigment Yellow 97 from CLARIANT.

PY110 is CHROMOPHTAL™ Yellow 3RT, a C.I. Pigment Yellow 110 from CIBASPECIALTY CHEMICALS.

PY111 is HANSA™ Brilliant Yellow 7GX, a C.I. Pigment Yellow 111 fromCLARIANT.

PY120 is NOVOPERM™ Yellow H2G, a C.I. Pigment Yellow 120 from CLARIANT.

PY128 is CHROMOPHTAL™ Jet Yellow 8GF, a C.I. Pigment Yellow 128 fromCIBA SPECIALTY CHEMICALS.

PY155 is NOVOPERM™ Yellow 4G, a C.I. Pigment Yellow 155 from CLARIANT.

PY170 is LYSOPAC™ Geel 7010C, a C.I. Pigment Yellow 170 from CAPPELLEPIGMENTS N.V.

PY176 is PERMANENT™ Yellow GRX 83, a C.I. Pigment Yellow 176 fromCLARIANT.

PY180 is TONER™ Yellow HG, a C.I. Pigment Yellow 180 from CLARIANT.

PY213 is INK JET™ Yellow H5G LP 3083, a C.I. Pigment Yellow 213 fromCLARIANT.

PBL7 is SPECIAL BLACK™ 550, a carbon black available from DEGUSSA.

PR202 is the abbreviation for C.I. Pigment Red 202 for which CINQUASIAMAG RT235D from CIBA SPECIALTY CHEMICALS was used.

Diethyl-5-(hydroxymethyl)isophthalate from ALDRICH.

DPGDA is dipropyleneglycoldiacrylate available under the trade name ofSARTOMER™ SR508 from SARTOMER.

SR9003 is an abbreviation for SARTOMER™ SR9003, a propoxylated neopentylglycol diacrylate monomer available from SARTOMER.

Vinylcaprolactam is

CRAYNOR™ CN 386 is an amine modified acrylate synergist available fromCRAY VALLEY.

GENOCURE™ EPD is ethyl 4-dimethylaminobenzoate available from RAHN AG.

ITX is 4-phenylbenzophenone, a photo-initiator available under the tradename of GENOCURE™ ITX from CIBA SPECIALTY CHEMICALS.

TPO is 2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide available underthe trade name DAROCUR™ TPO from CIBA SPECIALTY CHEMICALS.

BYK™ UV3510 is a polyethermodified polydimethylsiloxane wetting agentavailable from BYK CHEMIE GMBH.

BykSol is a 50% solution of BYK™ UV3510 in DPGDA.

ITX is a photo-initiator available under the trade name of DAROCUR™ ITXfrom CIBA SPECIALTY CHEMICALS.

GENORAD™ 16 is polymerization inhibitor from RAHN AG.

GenoSol is a 50% solution of GENORAD™ 16 in DPGDA.

GENOCURE™ PBZ is 4-phenylbenzophenone, a photo-initiator from RAHN AG.

SARTOMER™ 399 LV is a low viscosity dipentaerythritol pentaacrylate fromSARTOMER.

SOLSPERSE™ 35100 is a 40% polyethyleneimine core grafted with polyesterhyperdispersant solution in butyl acetate available from NOVEON.

S32000 is SOLSPERSE™ 32000, S33000 is SOLSPERSE™ 33000 and

S39000 is SOLSPERSE™ 39000, and these are all three solidpolyethyleneimine cores grafted with polyester hyperdispersant fromNOVEON.

DEGDEE is diethylene glycol diethylether from ACROS.

The quinacridone derivative QAD-3 is represented by the formula:

Synthesis of the dispersion synergist QAD-3 was accomplished accordingto the following synthesis scheme:

(0.1 mol) of dried pigment PR202 in 130 gram dimethylsulfoxide wasdissolved by the addition of 23 g (0.205 mol) potassium tert-butoxide.The blue-green solution was heated to about 110° C. for 1 hour. Then themixture was cooled till 40° C., and 25.5 g (0.105 mol) of compound QA-2was added. The alkylation-step was done after 4 hours. The product washydrolyzed by the addition of 400 ml of water and 19.5 gram Potassiumhydroxide 86% (0.3 mol) after 4 hours heating at 60° C. Then 75 mlconcentrated hydrochloric acid (0.9 mol) was added to the mixture. Thedispersion synergist QAD-3 was filtered and washed with water. The yieldwas 100%.

Synthesis of dimethyl-(5-chloromethyl)isophthalate (QA-2) wasaccomplished according to the following synthesis scheme

(0.1 mol) of dimethyl-(5-hydroxymethyl)isophthalate (QAOH-2) wasdissolved in a mixture of 100 mL of Toluene and 0.2 g dimethylacetamide(catalyst). 15.4 g (0.13 mol) of thionylchloride was added drop wise andthe mixture was stirred during 4 hour at 40° C. After this period, themixture was cooled in an ice bath and 50 mL of methanol was added. Thissolid product QA-2 was filtered and washed with a small volume ofmethanol. The yield was 58%.

Synthesis of dimethyl-(5-hydroxymethyl)isophthalate QOAH-2 wasaccomplished according to the following synthesis scheme

(0.1 mol) of trimethyl 1,3,5 benzenetricarboxylate was dissolved in 85mL of methyl acetate at 50° C. 40.5 ml (0.08 mol) lithiumborohydride 2.0M in THF was added drop wise and the mixture was stirred during 3 hourat 50° C. After this period 5.3 gram acetic acid (0.088 mol) and 3 mLwater were added. The methyl acetate and THF were evaporated, 50 mlwater and 50 ml n-hexane were added. The product QAOH-2 was filtered andwashed with a small volume water and n-hexane. The yield was 63%.

Measurement Methods

1. Measurement of SSF

The spectral separation factor SSF of an ink was calculated by using thedata of the recorded spectrum of an ink solution and comparing themaximum absorbance to the absorbance at a reference wavelength. Thechoice of this reference wavelength is dependent on the pigment(s) used:

-   -   if the colour ink has a maximum absorbance A_(max) between and        500 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 600 nm,    -   If the colour ink has a maximum absorbance A_(max) between and        600 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 650 nm,    -   If the colour ink has a maximum absorbance A_(max) between and        700 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 830 nm.

The absorbance was determined in transmission with a Shimadzu UV-2101 PCdouble beam-spectrophotometer. The inkjet inks were diluted with ethylacetate to have a pigment concentration according to Table 1.

TABLE 1 Inkjet ink with Pigment maximum absorbance A_(max) concentrationbetween 400 and 500 0.002% between 500 and 600 0.005% between 600 and700 0.002%

A spectrophotometric measurement of the UV-VIS-NIR absorption spectrumof the diluted ink was performed in transmission-mode with a doublebeam-spectrophotometer using the settings of Table 2. Quartz cells witha path length of 10 mm were used and ethyl acetate was chosen as ablank.

TABLE 2 Mode Absorbance Wavelength range 240-900 nm Slit width 2.0 nmScan interval 1.0 nm Scan speed Fast (1165 nm/min) Detectorphoto-multiplier (UV-VIS)

Efficient pigment inkjet inks exhibiting a narrow absorption spectrumand a high maximum absorbance have a value for SSF of at least 30.

2. Average Particle Size (BI90)

The average particle size diameter was determined with a BrookhavenInstruments Particle Sizer BI90plus based upon the principle of dynamiclight scattering. The ink or dispersion was diluted with ethyl acetateto a pigment concentration of 0.002 wt %. The measurement settings ofthe BI90plus were: 5 runs at 23° C., angle of 90°, wavelength of 635 nmand graphics=correction function.

3. Average Particle Size (Malvern)

The particle size of pigment particles in pigment inkjet ink wasdetermined by photon correlation spectroscopy at a wavelength of 633 nmwith a 4 mW HeNe laser on a diluted sample of the pigment inkjet ink.The particle size analyzer used was a MALVERN™ nano-S available fromGoffin-Meyvis.

The sample was prepared by addition of one drop of ink to a cuvetcontaining 1.5 mL ethyl acetate and mixed until a homogenous sample wasobtained. The measured particle size is the average value of 3consecutive measurements consisting of 6 runs of 20 seconds. For goodink jet characteristics (jetting characteristics and print quality) theaverage particle size of the dispersed particles is below 200 nm,preferably about 100 nm. The pigment inkjet ink is considered to be astable pigment dispersion if the particle size remained below 200 nmafter a heat treatment of 7 days at 80° C.

4. Viscosity

The viscosity of the inkjet inks was measured using a Brookfield DV-II+viscometer at 25° C. and shear rate of 15 RPM.

5. Pigment Dispersion Stability

The dispersion stability was evaluated by comparing the SSF before andafter a heat treatment of one week at 80° C. The decrease of SSF ofpigmented inkjet inks exhibiting good dispersion stability shouldpreferably be less than 15%.

6. W_(tot N)

The nitrogen content of a polymer was determined according to DINISO13878 (Bodenbeschaffenheit, Bestimmung des Gesamt-Stickstoffs durchtrockene Verbrennung).

7. N_(Amide)

The amine content N_(amine) of the polymeric dispersant, expressed asmol amine/100 g of polymeric dispersant, can be determined throughpotentiometric titration in a mixture of CH₃COOH:THF (14.5:0.5) with0.1N aqueous perchloric acid. The mole % nitrogen present as an amidebond N_(Amide) based upon the total nitrogen content W_(tot N) of thepolymeric dispersant is found by the following formula:N _(Amide)=100×[(W _(tot N)/14)−N _(amine) ]/[W _(tot N)/14]8. W_(TPOAC)

The W_(TPOAC) is calculated by the formula:W _(TPOAC)=[100−(N _(tot)×43)/14]/[N _(tot)−(N _(amine)×14)].

Example 1

This example illustrates the preparation of polymeric dispersants bycondensation of carboxylic acid terminated polyester and PEI.

Synthesis of the TPOAC-acid PE1

The TPOAC-acid PE1 (LA₁-εCap_(18.7)-co-δVal_(4.3)) was preparedaccording to the following procedure: a mixture of 66.0 g Lauric acid(0.15 mol, Acros Organics), 714.3 g epsilon Caprolactone (1.800 mol,Acros Organics) and 148.4 g delta Valerolactone (0.90 mol, AcrosOrganics) is heated to 100° C. and degassed with N₂ during 30 min. 3.45g Zirconium IV isopropoxide isopropanol complex (3.5 mmol, Aldrich) isadded and the mixture is heated to 170° C. After 6 hours stirring at170° C. the mixture is cooled.

Synthesis of the TPOAC-acid PE2

The TPOAC-acid PE2 (LA₁-εCap_(21.3)-co-δVal_(4.1)) was preparedaccording to the following procedure: a mixture of 85.0 g Lauric acid(0.15 mol, Acros Organics), 1041.0 g epsilon Caprolactone (1.800 mol,Acros Organics) and 233.6 g delta Valerolactone (0.90 mol, AcrosOrganics) is heated to 100° C. and degassed with N₂ during 30 min. 4.44g Zirconium IV isopropoxide isopropanol complex (3.5 mmol, Aldrich) isadded and the mixture is heated to 170° C. After 6 hours stirring at170° C. the mixture is cooled.

Synthesis of Polymeric Dispersant (PD1).

Polymeric dispersant PD1 was prepared according to the followingprocedure: a mixture of 1130.0 g TPOAC-acid PE1 and 87.0 gpolyethyleneimine (PEI) Epomin SP200 (Nippon Shokubai, molecular weight10000 g/mol on the label) is heated to 120° C. It is stirred for 6 hoursunder a constant N₂ flow. After 6 hours stirring at 120° C. the mixtureis cooled.

The polymeric dispersants PD2 to PD4 were prepared according to the sameprocedure, but using amounts (in g) as indicated in Table 3.

TABLE 3 wt ratio m_(PE) Polymeric TPOAC- graft/ m_(PEI) graft dispersantacid PEI (g) (g) PD1 PE1 13/1 87.0 1130.0 PD2 PE2 16.5/1   25.0 412.5PD3 PE2 13/1 30.0 390.0 PD4 PE2  6/1 65.0 390.0

Polymeric Dispersant S35000

SOLSPERSE™ 35100 is a hyperdispersant used in highly concentratedpaints. This hyperdispersant was only available as a 40 wt % solution inbutyl acetate.

This polymeric dispersant S35000 was obtained by a specific request tothe manufacturer, NOVEON, to deliver a batch of the same polymericdispersant SOLSPERSE™ 35100 but without addition of butyl acetate orother solvents.

Characterization of the Polymeric Dispersants

For each polymeric dispersant, the values were determined for N_(Amine)and N_(Amine.)he and subsequently the W_(TPOAC) and N_(Amide) werecalculated. The results are given by Table 4.

TABLE 4 N_(Amine) N_(Amide) (mole (mol % relative Polymeric W_(tot N)amine/100 g to total N- dispersant (wt % N) polymer) W_(TPOAC) content)PD1 2.3 0.0624 65 62 PD2 1.9 0.0446 74 67 PD3 2.4 0.0575 58 66 PD4 4.60.1320 31 60 S32000 2.5 0.0588 55 67 S39000 2.4 0.0521 55 70 S35000 2.00.0504 73 65

Example 2

This example illustrates that a range different organic solvents can beused to dilute a concentrated pigment dispersion of PY150.

Preparation of the Concentrated Pigment Dispersion

Two concentrated pigment dispersions were prepared in the same manner toobtain a composition as described in Table 5, except that in a firstdispersion the polymeric dispersant S39000 was used, while in the secondconcentrated dispersion the polymeric dispersant S35000 was used.

TABLE 5 Component wt % PY150 15 Polymeric 15 Dispersant DEGDEE 70

The concentrated pigment dispersion was made by mixing the 75.0 g ofpigment and 187.5 g of a 40% solution of the polymeric dispersant in theorganic solvent diethyleneglycol diethylether (DEGDEE) for 30 minutesusing a DISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg) andsubsequently milling this mixture in a NETZSCH Mini-Zeta (fromNETZSCH-CONDUX Mahltechnik GmbH) using yttrium-stabilized zirconiumoxide-beads of 0.4 mm diameter (“high wear resistant zirconia grindingmedia” from TOSOH Co.). The bead mill is filled with 900 g of thegrinding beads and water-cooled during milling at 2886 rpm for 45minutes. After milling the dispersion was separated from the beads usinga filter cloth.

The average particle size (BI90), SSF and viscosity was determined. Thetwo concentrated pigment dispersions prepared with the polymericdispersants S39000 and S35000 exhibited similar physical properties ascan be seen in Table 6.

TABLE 6 S39000 S35000 Physical Pigment Pigment property dispersiondispersion Viscosity 31 32 (mPa · s) SSF 56 57 Particle size 142 145(nm)

Inkjet inks were then prepared by diluting 4 g of the pigmentdispersions with 11 g of organic solvent S1 to S20 of Table 7.

TABLE 7 Solvent Organic solvents S1 Mesitylene (1,3,5- trimethylbenzene)S2 Chlorobenzene S3 n-amyl acetate S4 n-butylacetate S5n-butylglycolacetate (BGA) S6 Toluene S7 Carbotilacetate (DEGMEEA) S8DOWANOL ™ DPMA (DPGMMEA) S9 Dimethylphthalate S10 Diethylene glycoldibutyl ether (DEGDBE) S11 Tetraethyleneglycol dimethylether (TeEGDME)S12 Methyl acetate S13 Methylal S14 4-Heptanone S15Chlorobenzene/Amylacetate (50/50) S16 Toluene/Amylacetate (50/50) S17Chlorobenzene/DEGDEE (50/50) S18 Toluene/Chlorobenzene (50/50) S19DEGDEE/Cycloheptanone (50/50) S20 Cycloheptanone/Amylacetate (60/40)

Evaluation of the Inkjet Inks

The dispersion quality was evaluated after dilution of the concentratedpigment dispersions to inkjet inks by measuring the SSF and expressingthe result as a percentage loss in SSF after dilution from the pigmentdispersion. The ink sample was then given a heat treatment for 7 days at83° C. before the SSF was measured again. The percentage loss in SSFafter heat treatment with reference to the SSF of the inkjet ink isgiven in the second column “7d/83° C.” of Table 8.

TABLE 8 Inkjet ink Ink with S39000 Ink with S35000 diluted % Loss in %Loss in with SSF after SSF after solvent: dilution 7 d/83° C. dilution 7d/83° C. S1 0 81 2 0 S2 0 0 0 0 S3 0 65 1 3 S4 0 56 1 0 S5 0 52 0 0 S6 031 0 0 S7 0 5 1 0 S8 0 28 1 0 S9 0 0 37 0 S10 33 89 48 84 S11 0 14 0 0S12 0 4 0 0 S13 0 33 1 9 S14 0 66 2 8 S15 0 29 0 0 S16 0 58 0 0 S17 0 160 0 S18 0 3 40 0 S19 0 6 1 0 S20 0 0 0 0

From Table 8, it can be seen that the concentrated pigment dispersionsof PY150 using the polymeric dispersant S35000 can be diluted by a lotmore solvents for making inkjet inks without serious deterioration ofdispersion quality or stability.

Example 3

This example illustrates the effects of the design of the polymericdispersant on the quality and dispersion stability of inkjet inkscomprising PV19.

Preparation of Inkjet Inks

All inkjet inks were prepared in the same manner as described in Example2 except that the pigment PY150 was replaced by the quinacridone pigmentPV19 and that the polymeric dispersant PD1 to PD4, S32000, S35000 andS39000 were used to prepare concentrated pigment dispersions.

Evaluation of Inkjet Inks

The concentrated PV19 dispersions were diluted into inkjet inks S1 toS20 using the same organic solvents S1 to S20 of Example 2 in Table 7.

The dispersion quality of the inkjet inks was determined for each ink bycalculating the Spectral Separation Factor SSF. The results are shown inTable 9.

TABLE 9 Inkjet ink diluted SSF of inkjet ink with polymeric withdispersant: solvent PD3 PD2 PD1 PD4 S32000 S39000 S35000 S1 45 45 46 4542 39 45 S2 44 44 47 43 39 9 46 S3 44 44 47 47 41 40 45 S4 43 43 47 4643 42 45 S5 38 38 38 36 4 4 35 S6 43 43 47 51 43 36 45 S7 43 43 47 51 4443 46 S8 44 44 47 49 43 44 45 S9 42 42 46 55 21 8 44 S10 42 42 45 49 208 43 S11 42 42 47 51 29 8 45 S12 44 44 46 52 42 37 44 S13 43 43 46 52 4343 44 S14 42 42 47 59 43 40 43 S15 43 43 47 56 38 14 43 S16 44 44 47 5443 45 44 S17 43 43 47 57 44 47 44 S18 44 44 46 50 43 48 45 S19 42 42 4759 44 42 44 S20 40 40 45 51 42 8 43 # inkjet 20 20 20 20 17 13 20 inksout of 20 W_(TPOAC) 58 74 65 31 55 55 73 N_(Amide) 66 67 62 60 67 70 65

From Table 9, it is clear that dilution with some of the solventsresulted in an inferior dispersion quality, i.e. a SSF<30, for thecommercial dispersants S32000 and S39000. The row “# Inkjet inks out of20” indicates the number of inkjet inks out of the 20 inkjet inksprepared that exhibited good dispersion quality.

The inkjet inks were then given a heat treatment of 7 days at 83° C. toevaluate their dispersion stability. The dispersion stability isexpressed in % loss in SSF after heat treatment in Table 10.

TABLE 10 Inkjet % loss in SSF after 7 days at 83° C. ink PD3 PD2 PD1 PD4S32000 S39000 S35000 S1 8 8 30 23 12 56 0 S2 8 8 75 7 19 100 10 S3 5 5 52 14 21 2 S4 3 3 0 2 21 12 5 S5 1 1 85 0 100 100 0 S6 0 0 32 17 11 57 0S7 8 8 3 27 28 7 6 S8 6 6 6 10 15 33 3 S9 25 25 75 52 100 100 9 S10 7 771 82 100 100 35 S11 13 13 72 73 15 100 13 S12 8 8 37 76 36 50 0 S13 6 621 68 24 36 0 S14 8 8 17 66 45 48 29 S15 7 7 69 100 10 100 0 S16 1 1 11100 13 14 0 S17 2 2 41 100 30 36 18 S18 2 2 15 19 22 27 0 S19 18 18 1172 51 58 34 S20 19 19 74 69 56 100 15 # Inkjet 17 17 7 5 7 3 16 Inks outof 20 W_(TPOAC) 58 74 65 31 55 55 73 N_(Amide) 66 67 62 60 67 70 65

The row “Inkjet inks out of 20” indicates the number of inkjet inks outof the 20 inkjet inks prepared that exhibited good dispersion quality.Table 10 shows that only using the polymeric dispersant PD2, PD3 orS35000 having W_(TPOAC)>57 and N_(Amide)≧65 mol %, it was possible todilute the pigment dispersion into an inkjet ink with more than 15 outof the 20 different organic solvents without unacceptable deteriorationof dispersion stability.

Example 4

The polymeric dispersant can also be used to make a non-aqueouspigmented inkjet ink set. This example illustrates the preparation of anon-aqueous cyan inkjet ink containing C.I. Pigment Blue 15:4.

Preparation and Evaluation of Inkjet Inks

It was found that PB15:4 exhibited a similar behaviour as PY150, i.e.the polymeric dispersant allowed a wide variety of liquids for dilutinga concentrated pigment dispersion of PB15:4 into an inkjet ink. This isexemplified here below for radiation curable inkjet inks either lackingor comprising vinylcaprolactam as monomer. Vinylcaprolactam isespecially useful to include into a radiation curable inkjet ink whenthe printing is to be performed on a PVC substrate, because of itscapability of partly dissolving the PVC surface thereby improvingadhesion properties.

Two concentrated pigment dispersions of PB15:4 were prepared in the samemanner to obtain a composition as described in Table 11, except that ina first dispersion ‘A’ the polymeric dispersant S39000 was used as apolymeric dispersant, while in the second concentrated dispersion ‘B’the polymeric dispersant S35000 was used.

TABLE 11 Component wt % PB15:4 20 Polymeric 20 Dispersant GENORAD ™ 16 1DPGDA 49

The concentrated pigment dispersion was made by mixing 140.0 g of thecyan pigment, 14.0 g of GenoSol and 466.7 g of a 30% solution of thepolymeric dispersant in DPGDA for 30 minutes using a DISPERLUX™YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg) and subsequently millingthis mixture in a EIGER MINI MOTOR MILL (from Eiger Machinery, Inc.)using yttrium-stabilized zirconium oxide-beads of 0.4 mm diameter (“highwear resistant zirconia grinding media” from TOSOH Co.). The bead millis filled for 52% of the volume with the grinding beads and water-cooledduring milling for 90 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

The concentrated pigment dispersion ‘A’ having S39000 as polymericdispersant and concentrated pigment dispersion ‘B’ having S35000 aspolymeric dispersant were diluted with the components according to Table12 to obtain 4 inkjet inks A1, A2, B1 and B2.

TABLE 12 S39000 S35000 Component Ink A1 Ink A2 Ink B1 Ink B2 Dispersion‘A’ 15.0  15.0 — — Dispersion ‘B’ — — 15.0  15.0 DPGDA 68.0  51.0 68.0 51.0 Vinylcaprolactam — 17.0 — 17.0 GENOCURE ™ EPD 5.0 5.0 5.0 5.0 ITX5.0 5.0 5.0 5.0 TPO 5.0 5.0 5.0 5.0 GenoSol 1.8 1.8 1.8 1.8 BykSol 0.20.2 0.2 0.2

The dispersion quality was evaluated for the inks by measuring theviscosity at 45° C. and the average particle size (BI90) after thedilution of the concentrated pigment dispersion into an ink. Thedispersion stability on the inkjet inks A1, A2, B1 and B2 was evaluatedafter storing the inks for 7 days at 83° C. and measuring the viscosityat 45° C. and the average particle size (BI90) again. The results areshown in Table 13.

TABLE 13 After 7 days at 83° C. After dilution % increase InkjetViscosity Particle % increase in particle Ink (mPa · s) size (nm) inviscosity size A1 9.1 134 7 7 A2 8.1 135 32 128 B1 8.9 132 2 0 B2 8.1131 14 6

From Table 13 it can be seen that the dilution with a liquid carriereither lacking or containing vinylcaprolactam in the presence of S35000as polymeric dispersant exhibits minor differences in dispersionstability, contrary to the inks using S39000 as polymeric dispersant.

Example 5

This example illustrates that it is possible to prepare a non-aqueousradiation curable CMYK inkjet ink set with pigments and polymericdispersants in accordance with the present invention.

Preparation of Inkjet Inks

It was found also possible to make a stable black inkjet ink comprisingcarbon black as pigment and a magenta inkjet ink with a mixed crystal ofC.I. Pigment Violet 19 instead of PV19 as in Example 3. A dispersionsynergist QAD-3 was added to obtain an excellent dispersion quality andstability.

The radiation curable inkjet ink set was prepared according to Table 14.The concentrated pigment dispersions were made in the same manner asdescribed for the B1 ink comprising PB15:4 of Example 4, with theexception that different pigments were used in the other concentratedpigment dispersions.

TABLE 14 in wt % of ink K M C Y DPGDA 76.248 79.94  77.00  77.60  PBL72.25 — — — PV19/PR202 0.81 4.00 — — PB15:4 0.81 — 3.00 — PY150 — — —2.70 S35000 3.87 4.00 3.00 2.70 QAD-3  0.012 0.06 — — GENOCURE ™ EPD5.00 5.00 5.00 5.00 GENOCURE ™ PBZ 4.50 2.50 2.50 2.50 TPO 4.50 2.502.50 2.50 SARTOMER ™ 399 LV — — 5.00 5.00 BYK ™ UV 3510 1.00 1.00 1.001.00 GENORAD ™ 16 1.00 1.00 1.00 1.00

The CMYK ink set was evaluated on the single pass inkjet printer:DOTRIX™ from AGFA. The good dispersion stability of the inks wasreflected in a very reliable jetting performance of this ink set with nofailing printing nozzles during one week and a latency time of >100hours.

Example 6

This example illustrates that non-aqueous inkjet inks comprising a C.I.Pigment Yellow 150 exhibits superior dispersion stability and qualitycompared to other type of yellow pigments.

Preparation of Inkjet Inks

All inkjet inks were prepared in the same manner as in EXAMPLE 2, exceptthat different yellow pigments were used in combination with the samepolymeric dispersant S35000. The average particle size (Malvern) and theviscosity was determined.

TABLE 15 Average Particle Viscosity Pigment Size (nm) (mPa · s) PY150145 32 PY4 flocculated PY12 flocculated PY14 flocculated PY74flocculated PY81 flocculated PY83 flocculated PY93 flocculated PY95flocculated PY97 flocculated PY110 flocculated PY111 flocculated PY128flocculated PY155 flocculated PY170 flocculated PY176 flocculated PY213flocculated

From Table 15, it was surprising to see that only PY150 could bedispersed into a non-aqueous inkjet ink using the polymeric dispersantS35000, contrary to many other pigments.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

The invention claimed is:
 1. A non-aqueous inkjet ink comprising: C.I.Pigment Yellow 150; a dispersion medium; and a polymeric dispersantaccording to Formula (I):

wherein T represents hydrogen or a polymerization terminating group; Zrepresents the residue of hyperbranched polyethyleneimine having anumber-average molecular weight of at least 100; A represents one ormore oxyalkylene carbonyl groups selected from the group consisting ofoxyalkylene carbonyl groups derivable from δ-valerolactone,ε-caprolactone, and C₁₋₄-alkyl substituted ε-caprolactone; T-C(O)A_(n)-represents a TPOAC-chain which is bound to Z through an amide bond; andn and m are integers wherein m is at least 2 and n is from 2 to 100; andthe polymeric dispersant satisfies the conditions of:W _(TPOAC)>57 and N _(Amide)≧65 mol % wherein W_(TPOAC) represents aratio of a weight percentage of the TPOAC-chains over a weightpercentage of the amide bonds in the polymeric dispersant; N_(Amide)represents the mol % of the amide bonds based on a total nitrogencontent of the polymeric dispersant; and the values of W_(TPOAC) andN_(Amide) are calculated from the total nitrogen content determined bydry combustion of the polymeric dispersant and from the amine contentdetermined through potentiometric titration in a mixture of CH₃COOH:THF(14.5:0.5) with 0.1N aqueous perchloric acid.
 2. The non-aqueous inkjetink according to claim 1, wherein a chain moiety represented by -A_(n)-is a mixture of oxyalkylene carbonyl groups derivable fromδ-valerolactone and ε-caprolactone.
 3. The non-aqueous inkjet inkaccording to claim 2, wherein the mixture contains more than 75 mol %ε-caprolactone.
 4. The non-aqueous inkjet ink according to claim 2,wherein the alkyl substituent of C₁₋₄ alkyl substituted ε-caprolactoneis methyl.
 5. The non-aqueous inkjet ink according to claim 1, wherein Tis derived from a mono-carboxylic acid T-COOH selected from the groupconsisting of an aliphatic acid, an aromatic acid, a hetero-aromaticacid, a heterocyclic acid, and an alicyclic acid.
 6. The non-aqueousinkjet ink according to claim 5, wherein the aliphatic acid is a C₁₋₂₅aliphatic carboxylic acid optionally substituted by hydroxyl, C₁₋₄ alkylor halogen.
 7. The non-aqueous inkjet ink according to claim 1, furthercomprising a radiation curable compound.
 8. A non-aqueous inkjet ink setcomprising: at least one non-aqueous inkjet ink including: C.I. PigmentYellow 150; a dispersion medium; and a polymeric dispersant according toFormula (I):

wherein T represents hydrogen or a polymerization terminating group; Zrepresents the residue of hyperbranched polyethyleneimine having anumber-average molecular weight of at least 100; A represents one ormore oxyalkylene carbonyl groups selected from the group consisting ofoxyalkylene carbonyl groups derivable from δ-valerolactone,ε-caprolactone, and C₁₋₄-alkyl substituted ε-caprolactone; T-C(O)A_(n)-represents a TPOAC-chain which is bound to Z through an amide bond; andn and m are integers wherein m is at least 2 and n is from 2 to 100; thepolymeric dispersant satisfies the conditions of:W _(TPOAC)>57 and N _(Amide)≧65 mol % wherein W_(TPOAC) represents aratio of a weight percentage of the TPOAC-chains over a weightpercentage of the amide bonds in the polymeric dispersant; N_(Amide)represents the mol % of the amide bonds based on a total nitrogencontent of the polymeric dispersant; and the values of W_(TPOAC) andN_(Amide) are calculated from the total nitrogen content determined bydry combustion of the polymeric dispersant and from the amine contentdetermined through potentiometric titration in a mixture of CH₃COOH:THF(14.5:0.5) with 0.1N aqueous perchloric acid.
 9. The non-aqueous inkjetink set according to claim 8, wherein the ink set includes a secondnon-aqueous inkjet ink comprising C.I. Pigment Violet 19 or a mixedcrystal thereof.
 10. The non-aqueous inkjet ink set according to claim8, wherein the ink set includes a non-aqueous inkjet ink comprising C.I.Pigment Blue 15:4.